Guangfei Ding

Coercivity enhancement of sintered Nd-Fe-B magnets by chemical bath deposition of TbCl3

The chemical bath deposition (CBD) and the grain boundary diffusion method were combined to diffuse the heavy rare earth for obtain the thick magnets with high coercivity and low heavy rare earth. The jet mill powders were soaked into the alcohol solution of 0.2 wt. % TbCl3. A thin layer of TbCl3 was wrapped to the surface of (PrNd)2Fe14B powder particles. The coercivity of magnet is increased from 11.89 kOe to 14.72 kOe without significant reduction of remanence after grain boundary diffusion in the sintering and the annealing processes. The temperature coefficients of the remanence and the coercivity are improved by the substitution of PrNd by Tb in the surface of grains. The highly accelerated temperature/humidity stress test (HAST) results indicate that the CBD magnet has poor corrosion resistance, attributing to the present of Cl atoms in the grain boundaries.

Coercivity enhancement of Ce-Fe-B sintered magnets by low-melting point intergranular additive

Abstract Ce-Fe-B sintered magnets with enhanced coercivity were prepared by the powder metallurgy method. The mechanism of the coercivity enhancement in Ce-Fe-B sintered magnets with the low-melting point intergranular additive was discussed in details. It was speculated that the low coercivity of Ce-Fe-B sintered magnet was related to the irregular sharps and relatively low magneto-anisotropy field of the matrix phase. After introducing a 20 wt.% Nd-based intergranular additive, the coercivity markedly increased from 108 Oe to 2560 Oe due to the formation of thin and continuous grain boundary layers and the surface modification of the matrix phase grains. Additionally, the formation of the high anisotropy field (Nd,Ce) 2 Fe 14 B shell was beneficial to the increase of the coercivity as well. This work suggested that adding low-melting point intergranular additives was effective to fabricate the practical Ce-Fe-B sintered magnets.

Enhanced Thermal Stability of Nd–Fe–B Sintered Magnets by Intergranular Doping Y 72 Co 28 Alloys

The intergranular addition process using Y₇₂Co₂₈ eutectic alloy powders has been applied to (Pr, Nd)₂₇Dy₄Fe_67.65Cu_0.15Al_0.2B₁(wt.%) sintered magnets, resulting in an enhanced thermal stability. It was found that the coercivity of magnets at 100 °C increased while the addition of Y₇₂Co₂₈ is 1 wt.%, whereas the magnetic properties decreased slightly at room temperature due to lower magnetocrystalline anisotropy field (H_A ) of Y₂Fe₁₄B. The temperature coefficient of remanence (α ) and coercivity (β) for the magnets improved significantly. Microstructure observation indicated that Y atoms prefer to enter into the 2-14-1 phase and form a core-shell structure with an outer layer of (Nd, Dy, Y)₂(Fe, Co)₁₄B. Magnetic domain and intrinsic properties analysis suggested that the improved thermal stability resulted from the modified grain boundaries and the introduction of Y in matrix phases.